The aim of the work described in this proposal is to test directly the hypothesis that an endogenous electrical field in the chick embryo acts to guide lumbo-sacral neural crest cells to their targets in the hind gut. Dr. Robinson will do this by manipulating the endogenous field during the period of crest cell migration. This field, which is the result of a large current that leaves the posterior intestinal portal, will be altered by shunting the current which generates it through wounds created in the integument, or by voltage clamping the embryonic transepithelial potential, thus eliminating or reversing the endogenous field. The fluorescent dye DiI will be used to trace the neural crest cells during their migration. Dr. Robinson will also do a light and electron microscopy study of tail gut degeneration in the chick in order to establish that this process is responsible for the currents he detects leaving the posterior intestinal portal. The in vitro effects of an applied electrical field on the proposed endogenous field target cells will also be examined. He will extend his vibrating probe observations to mouse embryos, particularly some of the mutants that are available, in order to determine if changes in any of the endogenous current parameters are indicative of specific abnormalities. The information gained from these experiments will add substantially to our knowledge of how migratory cells are guided during development.
